1. Field of the Invention
The invention relates to a device for non-contacting measurement of a distance and/or of a profile of a measured object, whereby a light source generates an illumination light beam to illuminate the measured object and whereby a detector is provided for detection of the reflected portion of the illumination light beam at the measured object. The invention also relates to a corresponding method.
2. Description of Related Art
Devices of this type for non-contacting measurement of a distance and/or of a profile have been known for a long time from practice. In this process, a light source generates an illumination light beam that has been prepared by means of an optics. The illumination light beam is directed to a measured object and illuminates the measured object in the form of points. Portions of the illumination light beam reflected on the measured object are detected by a detection device of the sensor and from this a conclusion is made regarding the distance of the measured object from the sensor.
Very frequently sensors of this type work according to the triangulation principle. In this case, the illuminated point of the detector array changes due to the reflected portion of the illumination light beam depending on the distance of the measured object from the sensor. For determining the distance, a relationship is produced between the illuminated detector element and the distance of the measured object. In principle, this can also be calculated from the sensor geometry. However, usually calibration measurements are performed and the correlation between distance and illuminated spot are stored.
To improve the sensitivity of the sensor devices, giving the illumination light beam a slight linear expansion is known. Line lengths in the range from 2 to 3 mm are usual. This takes into account the fact that frequently detector arrays with rectangular detector elements are used. For spot-shaped illumination, usually the entire available surface of the detector elements is not used, but only a part of the elements are illuminated. The illuminated surface of a detector element can be increased by forming the illumination line and by suitable adaptation of the sensor device. Because of this, the sensitivity of the entire sensor device can be increased.
A sensor of this type is known from DE 10 2007 050 097 A1. This has a structured front disc that expands a bundled light beam generated by a light source in at least one direction. A first lens focuses the light beam emitted from the light source. The front disk, with several optical elements, is arranged between the lens and its focal point turned away from the light source. This generates a narrow, approximately parallel illumination light beam. Various possible implementations are named as optical elements, e.g. cylinder or spherical lenses, lens sections thereof, for example with Fresnel lenses, or aperture or grid structures. By mounting the optical elements on the front disk, the effort for calibrating the light source, optics and housing with respect to each other is reduced.
A very similar sensor structure is shown in DE 10 2007 050 096 A1. In addition, means are used to homogenize the light beam.
What is disadvantageous in these designs is that the optical characteristics of the sensor are not independent of mechanical stresses on the sensor. If the comparatively large front disk is mechanically stressed, it deforms and the optical characteristics of the sensor change. It is also problematic that with a defective front disk, after it is replaced new calibration measurements are necessary since the optical characteristics of the new front disk are not identical to those of the previously used front disk. Thus, the costs of operation increase.
For determining a profile of the measured object, multidimensional information regarding the measured object must be available. For this purpose, usually the triangulation sensor or the measured object is moved and the measured object is scanned in succession. In this case, the illumination light beam is generally moved in a meandering pattern over the measured object. The disadvantage here is that the scanning process is very time-consuming and because of this it is unsuitable in many application areas, for example during the measurement of profiles of vehicle tires.
Other solutions use an illumination light beam that illuminates the measured object in a linear shape. To prevent a bulky and heavy sensor optics, usually a divergent illumination light beam is used. With highly structured measured objects, however, this leads to shadowing of individual areas on the measured object, which means that no reliable measurement of these measured objects is possible. Another system, like the sensor described in DE 10 2007 050 097 A1, could in fact be adapted to a two-dimensional measurement of a measured object by elongating the illumination line, but because of this, very large optics would result. In addition, an approximately uniform intensity of the illumination along the illumination line can only be implemented with great effort, for example the use of means for homogenizing the light beam.
Therefore, the present invention is based on the object of indicating a compact sensor device that can be used in many ways, by means of which a reliable two-dimensional measurement of a measured object is made possible. A corresponding method will be indicated.